The present invention relates to an apparatus for cutting a metal sheet. More specifically, the present invention relates to such an apparatus as a slitter, a side-trimmer or the like suitably used for cutting an elongated metal sheet along the length thereof.
FIGS. 1 and 2 show a conventional side-trimmer for cutting a metal sheet or a metal sheet. The side-trimmer comprises a pair of cutter heads 1 (only one of the two heads is shown) which are arranged symmetrically to each other with respect to a vertical plane of symmetry CL of the side-trimmer. The pair of cutter heads 1 are mounted on a table 2 for linear sliding movement toward and away from each other in such a manner that horizontal distance between the cutter heads 1 is adjusted to cut off the opposite side edges of the metal sheet for dimensionning the sheet to a predetermined width. The metal sheet to be trimmed passes horizontally in a transit plane PL, so that a center line of the sheet generally coincides with the plane of symmetry CL.
Each of the cutter heads 1 includes a pair of upper and lower holder shafts 3 and 4 which are arranged perpendicular to the plane of symmetry CL and in parallel relation to each other in a vertical plane. A pair of upper and lower circular cutting blades 5 and 6 are detachably mounted to the forward ends of the holder shafts 3 and 4 for rotation therewith, the forward ends being on the side of the plane of symmetry CL. The cutting blades 5 and 6 are so disposed that the uppermost point of the lower cutting blade 6 comes slightly higher than the lowermost point of the upper cutting blade 5 and a surface of the lower cutting blade 6 opposite to the plane of symmetry CL and a surface of the upper cutting blade 5 facing to the plane of symmetry CL is generally in a same plane parallel to the plane of symmetry CL. When the holder shafts 3 and 4 are driven rotatively, the cutting blades 5 and 6 are rotated and cooperate with each other to cut the side edge of the metal sheet passing therebetween. In this manner, side-trimming of a metal sheet or a metal sheet is carried out.
Holder section 3a and 4a are formed on the forward ends of the respective upper and lower holder shafts 3 and 4. The cutting blades 5 and 6 are fitted respectively on the holder sections 3a and 4a of the upper and lower holder shafts 3 and 4. A nut-type fastener 7 is threadedly engaged with the forward end of the upper holder shaft 3 to tightly clamp the upper cutting blade 5 between the fastener 7 and a reference surface 3b. The reference surface 3b is formed on the holder section 3a perpendicular to an axis of the holder shaft 3. Likewise, the lower cutting blade 6 is tightly clamped between a nut-type fastener 8 and a reference surface 4b of the lower holder section 4a.
The upper holder shaft 3 is rotatably supported by an upper chock 9 through a pair of axially spaced tapered roller bearings 9a and 9a. The upper chock 9 is mounted to an upper portion of the cutter head 1 for vertical sliding movement. Likewise, the lower holder shaft 4 is rotatably supported by a lower chock 10 through a pair of axially spaced tapered roller bearings 10a and 10a. The lower chock 10 is mounted to a lower portion of the cutter head 1 for vertical sliding movement. A gap adjusting bolt 11, extending vertically, is connected to an upper portion of the upper chock 9 in threadedly engaged relation thereto. A worm shaft 12 is in mesh with a worm wheel (not shown) which is mounted to the gap adjusting bolt 11 for rotation therewith. The arrangement is such that when the worm shaft 12 is rotatively driven, the upper chock 9 is moved vertically, making it possible to adjust the amount of vertical gap between the upper and lower cutting blades 5 and 6 which are mounted, respectively, to the upper and lower holder shafts 3 and 4.
That is, when it is desired to adjust the amount of vertical gap between the upper and lower cutting blades 5 and 6 in each of both the cutter heads 1 (only one shown) in compliance with the thickness of the metal sheet to be side-trimmed, a rotary shaft 13 extending between upper portions of the respective cutter heads 1 is rotated by a wheel 13a, whereby the mounts of vertical lap in the respective cutter heads 1 are adjusted simultaneously. Specifically, when the rotary shaft 13 is rotatively driven by the wheel 13a, rotation of the rotary shaft 13 is transmitted to the worm shaft 12 through a chain 14. The gap adjusting bolt 11 is rotatively driven through the worm wheel in mesh with the worm shaft 12, so that the upper chock 9 is moved vertically. On the other hand, a vertical position adjusting wedge 15 is arranged below the lower chock 10. When a wedge drive screw 16 arranged horizontally is rotated by a wheel 16a, the wedge 15 is moved in a direction perpendicular to the transit direction of the metal sheet, i.e., toward and away from the plane of symmetry CL. This causes the lower chock 10 to be moved vertically. The vertical positions of the respective upper and lower cutting blades 5 and 6 are adjusted in the following manner. That is, the amount of downward adjustment of the upper cutting blade 5 and the amount of upward adjustment of the lower cutting blade 6 are made equal to each other. The transit plane of the metal sheet is brought to a position where the amount of vertical gap between the upper and lower cutting blades 5 and 6 is divided into two equal distances. Specifically, the transit plane of the metal sheet is brought to the vertical position of the pass plane PL. In other words, if the upper and lower cutting blades 5 and 6 are equal in diameter to each other, the vertical distance between the pass plane PL and the upper holder shaft 3 is made equal to that between the pass plane PL and the lower holder shaft 4, so that the transit plane of the metal sheet is brought into coincidence with the pass plane PL.
The side-trimmer further comprises a drive system for rotatively driving the upper and lower holder shafts 3 and 4. The drive system includes a drive shaft 17 arranged at the same level as the lower holder shaft 4 in parallel relation thereto, as shown in FIG. 2. A drive gear 19 is mounted on the drive shaft 17 for rotation therewith. The drive gear 19 is in mesh with a driven gear 18 which is mounted on the lower holder shaft 4 for rotation therewith and which is arranged within the lower chock 10 substantially at an axial center thereof. Rotation of the drive shaft 17 is transmitted to the lower holder shaft 4 directly through the gears 19 and 18. On the other hand, the gear 19 is in mesh with an intermediate gear 19a which, in turn, is in mesh with a driven gear 20. The driven gear 20 is mounted on the upper holder shaft 3 for rotation therewith and is arranged within the upper chock 9 substantially at an axial center thereof. Rotation of the drive shaft 17 is transmitted to the holder shaft 3 through the gears 19, 19a and 20. In this manner, the upper and lower holder shafts 3 and 4 are rotatively driven by the drive shaft 17 at equal rotational speed. The side edge of the metal sheet is caused to pass between the upper and lower cutting blades 5 and 6 which are rotated respectively by the holder shafts 3 and 4, whereby the side edge of the metal sheet is cut by the upper and lower cutting blades 5 and 6. In the manner described above, the side-trimming is carried out with respect to the opposite side edges of the metal sheet by the pair of cutter heads 1.
In the above conventional side-trimmer, when it is desired to increase the amount of vertical gap between the upper and lower cutting blades 5 and 6 in compliance with the thickness of the metal sheet, the upper chock 9 supporting the upper holder shaft 3, having mounted thereto the upper cutting blade 5, is first moved downward by a distance half of the desired amount of vertical gap. Subsequently, the lower chock 10 supporting the lower holder shaft 4, having mounted thereto the lower cutting blade 6, is moved upwardly by the distance half of the desired amount of vertical gap, so as to bring the pass plane PL of the side-trimmer into coincidence with the transit plane of the metal sheet. In this manner, it is required for the conventional side-trimmer to adjust the vertical positions of the respective holder shafts 3 and 4 independently of each other, in order to adjust the amount of vertical gap between the upper and lower cutting blades 5 and 6.
Conventional side-trimmers have problems and inconveniences which will be explained as follows.
It is required that the cut surface of the metal sheet is as flat and smooth as possible in order to avoid cracking and fissuring of the metal sheet during subsequent processes. If the cut surface is not enough flat and smooth, fissuring and cracking occur in the metal sheet during subsequent operations such as rolling, other plastic forming etc and the fissure and cracks may expand to break the metal sheet. For that, the metal sheet have to be shear-cut by the cutting blades. On the contrary, the metal sheet must not be ruptured. Further, it is desirable to minimize plastic deformation remaining on the cut edge of the metal sheet. In order to realize the above-mentioned cutting of the metal sheet, it is required that the cutting blades has a most flat cutting plane and that the cutting blades are retained so that the cutting plane are exactly coincident with a plane when they are assembled in the side-trimmer. A problem as to conventional side-trimmers are that they do not have such exactitude in cutting metal sheets because of the gaps and inexactitudes residing inevitably therein. The cause of the inexactitudes exists, for example, in the mechanism for adjusting the vertical gap, mechanism for holding the cutting blades, mechanism for holding the holder shafts, etc. which will be explained in more detail later.
In the conventional side-trimmer, the upper and lower chocks 9 and 10 are arranged for vertical sliding movement relative to a housing 1ain order to adjust the amount of vertical lap between the upper and lower cutting blades 5 and 6. Accordingly, clearances exist between the upper and lower clocks 9 and 10 and the housing 1a in order to enable the sliding movement of the upper and lower chocks 9 and 10 at the adjustment of the amount of vertical gap. Because of such clearance, it is difficult to raise the accuracy of the degree of parallelism between the upper and lower holder shafts 3 and 4 and the degree of perpendicularly of the upper and lower holder shafts 3 and 4 with respect to the plane of symmetry CL. Moreover, since the upper chock 9 is moved vertically by the gap adjusting bolt 11 to adjust the amount of vertical gap between the upper and lower cutting blades 5 and 6, backlash of the gap adjusting bolt 11 causes errors, resulting in a deterioration of the accuracy in the adjustment of the amount of vertical gap.
One of the other problems is that the adjusting operation is elaborating, even not being sufficiently exact and takes a considerable time for the adjusting operation.
The above-described side-trimmer comprising the pair of upper and lower cutting blades 5 and 6 has conventionally been employed as a metal sheet cutting apparatus capable of obtaining a mirror-like high cut dimension accuracy. In the metal sheet cutting apparatus of the kind referred to above, cutting is performed with the pair of upper and lower cutting blades 5 and 6 set in such a manner that a predetermined horizontal gap is defined between the upper and lower cutting blades 5 and 6 in accordance with the thickness of the metal sheet to be cut. Because of such arrangement, a cut surface of the metal sheet consists of a shear surface section formed on, for example, 50% of the sheet thickness and a broken surface section formed on the remaining 50% of the sheet thickness. In the conventional apparatus so designed as to be suitable for the cutting operation under such condition, the cut dimension accuracy is of the order of 2/100 to 5/100 mm in error, even in case where the accuracy is good.
On the other hand, an increase in uses of the metal sheet material has produced a necessity of cutting at a cut dimension accuracy within a range of from 2/100 to 3/1000 mm in error. In recent years, a demand from the user has increased for supply of the metal sheet material cut at such high accuracy.
It is impossible for the conventional cutting apparatus in which the broken surface section is formed on a part of the cut surface, however, to achieve the cutting at the high accuracy within the range of from 2/1000 to 3/1000 mm in error. It is required for the cutting at such high accuracy to cut the metal sheet material such that the cut surface consists of a shear surface section formed substantially on 100% of the sheet thickness, and a broken surface section is not almost formed on the cut surface. For this purpose, it is a necessary minimum condition that the amount of horizontal gap between the rotating upper and lower cutting blades 5 and 6 is brought close to 0 (zero) mm as far as possible.
In the conventional metal sheet cutting apparatus such as, for example, the side-trimmer described above, each of the circular upper and lower cutting blades 5 and 6 is fixedly mounted to a corresponding one of the holder shafts 3 and 4 in such a manner that the one end face of the cutting blade 5 or 6 is abutted against the vertical holder reference surface 3b or 4b formed on the holder section 3a or 4a of the holder shaft 3 or 4, thereby obtaining the requisite degree of perpendicularity of the cutting blade 5 or 6 with respect to the holder shaft 3 or 4. Specifically, as described previously, the nut-type fasteners 7 and 8 are threadedly engaged respectively with the male threads formed on the forward ends of the respective holder shafts 3 and 4. The one end faces of the respective upper and lower cutting blades 5 and 6 are abutted respectively against the holder reference surfaces 3b and 4b, thereby fixing the upper and lower cutting blades 5 and 6. Accordingly, it is inevitable that each of the nut-type fasteners 7 and 8 urges a corresponding one of the upper and lower cutting blades 5 and 6 against a corresponding one of the holder reference surfaces 3b and 4b in an inclined posture of the nut-type fastener 7 or 8 because of the lead angle and the backlash of the male threads formed on the holder shaft 3 or 4. Thus, a part of the end face of the upper or lower cutting blade 5 or 6 is abutted against the holder reference surface 3b or 4b so that the each cutting blade 5 or 6 is fastened in an inclined fashion. As a result, the requisite degree of perpendicularity of the upper and lower cutting blades 5 and 6 with respect to the respective holder shafts 3 and 4 cannot be obtained.
Since the upper and lower cutting blades 5 and 6 are fastened in a slightly inclined fashion with respect to the respective holder shafts 3 and 4, run-out occurs in each of the upper and lower cutting blades 5 and 6, when the holder shafts 3 and 4 are rotated. Accordingly, unless an appropriate horizontal gap is left between the upper and lower cutting blades 5 and 6, they interfere with each other, resulting in such an anxiety that the cutting blades are broken or are brought to a state incapable of rotation. Thus, it is impossible to set the amount of horizontal gap to 0 mm.
Further, in case where the upper and lower cutting blades 5 and 6 are fastened in an inclined fashion with respect to the respective holder shafts 3 and 4, run-out occurs when the upper and lower cutting blades 5 and 6 are rotated. This run-out results in an error of the cut dimension.
Moreover, as described previously, the clearances are defined between the upper and lower chocks 9 and 10 and housing 1a, in order to enable the sliding movement of the upper and lower chocks 9 and 10 at the adjustment of the amount of vertical lap between the upper and lower cutting blades 5 and 6. Accordingly, the upper and lower chocks 9 and 10 are rickety, because of the clearances, so that deviation occurs in the parallelism and the vertical alignment between the upper and lower holder shafts 3 and 4 in the vertical plane. As a consequence, it is required for the upper and lower cutting blades 5 and 6 to have an appropriate horizontal gap therebetween, in order to avoid the interference between the upper and lower cutting blades 5 and 6.
Furthermore, in the conventional metal sheet cutting apparatus such as the side-trimmer as described above, the upper and lower holder shafts 3 and 4 are rotatively driven in the following manner. That is, the driven gears 18 and 20 are mounted respectively on the holder shafts 3 and 4 for rotation therewith. The drive shaft 17 having mounted thereon the drive gear 19 is arranged within the same housing 1a. Rotation of the drive shaft 17 is transmitted directly or indirectly to both the driven gears 18 and 20, thereby rotatively driving the holder shafts 3 and 4. In such arrangement, a load is applied from the rotating drive gear 19 and intermediate gear 19a to the driven gears 18 and 20 at running of the cutting apparatus, so that deflection occurs in each of the upper and lower holder shafts 3 and 4. As a result, the degree of perpendicularity of each of the upper and lower cutting blades 5 and 6 with respect to the axis of a corresponding one of the holder shafts 3 and 4 varies. Thus, it is required for the upper and lower cutting blades 5 and 6 to have an appropriate amount of horizontal gap therebetween, in order to eliminate interference between the upper and lower cutting blades 5 and 6.
Further, in the conventional metal sheet cutting apparatus such as the side-trimmer described above, each of the holder shafts 3 and 4 is supported rotatably in such a manner that the radial load and the thrust load acting upon the holder shaft 3 or 4 are born by the tapered roller bearings 9a or 10a which are large in play in the thrust direction. Accordingly, when the load is applied to the rotating upper and lower cutting blades 5 and 6 at cutting of the metal sheet, the upper and lower cutting blades 5 and 6 tend to move away from each other. Thus, the holder shafts 3 and 4 axially move independently of each other within the range of the thrust play of the tapered roller bearings 9a and 10a, so that the amount of horizontal gap between the upper and lower cutting blades 5 and 6 is varied. Thus, even if the amount of horizontal gap is adjusted and set beforehand to 0 mm, the horizontal gap is enlarged at the cutting of the metal sheet.
Moreover, because of the aforesaid clearances between the upper and lower chocks 9 and 10 and the housing a, the load acting upon the upper and lower cutting blades 5 and 6 at the running of the side-trimmer causes the holder shafts 3 and 4 to be moved axially. Thus, each of the upper and lower chocks 9 and 10 is urged axially and is moved axially within the range of the amount of clearance. As a result, the horizontal gap between the upper and lower cutting blades 5 and 6 is further enlarged.
Furthermore, in case where the upper and lower cutting blades 5 and 6 are fastened in such a manner that the upper and lower cutting blades are slightly inclined with respect to the respective holder shafts 3 and 4 as described previously, deviation occurs in each of the upper and lower cutting blades 5 and 6 when they are rotated. The deviation results in an error in the cut dimension.